1. Field of the Invention
The present invention relates to a radar device that irradiates an observation area where a required maximum distance different in each azimuth is assumed with waves, and uses a transmission antenna having directivity characteristics that are set on the basis of distance attenuation characteristics in which the transmission gains in the respective azimuths are set on the basis of the distance attenuation characteristics at the required maximum distances.
2. Description of the Related Art
Up to now, there has been known a radar device of a digital beam forming (DBF) system (for example, refer to Merrill I. Skolnik, Introduction to Radar Systems, Third Edition, pp. 610 to 615, McGraw-Hill, 2001). In the radar device of the DBF system, electric waves are transmitted by an antenna having a wide beam width, and a plurality of receiving beams having a narrow beam width a recombined together within an electric wave irradiated area to detect a target.
According to the radar device of the DBF system, since the beams for reception are logically combined with each other, it is possible to conduct radar observation in a plurality of directions at the same time. For example, in the case of the radar that conducts mechanical scan with antenna beams, because the plurality of directions are measured in time division, there occurs a difference in observation time depending on the observation directions. However, the DBF system does not suffer from such a problem. Also, in the case of measuring the wide angle range, a period of time during which scanning is conducted by the antenna in one cycle becomes a time resolution per one direction in the mechanical scan antenna. Accordingly, the time resolution is subjected to the mechanical limit of the antenna scan. On the contrary, in the DBF system, because it is unnecessary to conduct the mechanical scan, the observation can be repeated in a short time, that is, observation can be conducted with a high time resolution, within a range that is permitted by the detection performance.